This invention relates to fiber waveguides, and more particularly to high index-contrast fiber waveguides.
Optical components are becoming increasingly more common in telecommunication networks. For example, fiber waveguides such as optical fibers are used to carry information between different locations as optical signals. Such waveguides substantially confine the optical signals to propagation along a preferred path or paths. Similarly, other components such as sources, modulators, and converters often include guided regions that confine electromagnetic (EM) energy. Although metallic waveguides have a long history of use at longer wavelengths (e.g., microwaves), their usefulness as waveguides in the optical regime (e.g., 350 nm to 3 microns) is limited by their absorption. Thus, dielectric waveguiding regions are preferred in many optical applications.
The most prevalent type of fiber waveguide is an optical fiber, which utilizes index guiding to confine an optical signal to a preferred path. Such fibers include a core region extending along a waveguide axis and a cladding region surrounding the core about the waveguide axis and having a refractive index less than that of the core region. Because of the index-contrast, optical rays propagating substantially along the waveguide axis in the higher-index core can undergo total internal reflection (TIR) from the core-cladding interface. As a result, the optical fiber guides one or more modes of electromagnetic (EM) radiation to propagate in the core along the waveguide axis. The number of such guided modes increases with core diameter. Notably, the index-guiding mechanism precludes the presence of any cladding modes lying below the lowest-frequency guided mode for a given wavevector parallel to the waveguide axis. Almost all index-guided optical fibers in use commercially are silica-based in which one or both of the core and cladding are doped with impurities to produce the index contrast and generate the core-cladding interface. For example, commonly used silica optical fibers have indices of about 1.45 and index contrasts ranging from about 0.2% to 3% for wavelengths in the range of 1.5 xcexcm, depending on the application.
Drawing a fiber from a preform is the most commonly used method for making fiber waveguides. A preform is a short rod (e.g., 10 to 20 inches long) having the precise form and composition of the desired fiber. The diameter of the preform, however, is much larger than the fiber diameter (e.g., 100xe2x80x2s to 1000xe2x80x2s of times larger). Typically, when drawing an optical fiber, the material composition of a preform includes a single glass having varying levels of one or more dopants provided in the preform core to increase the core""s refractive index relative to the cladding refractive index. This ensures that the material forming the core and cladding are rheologically and chemically similar to be drawn, while still providing sufficient index contrast to support guided modes in the core. To form the fiber from the preform a furnace heats the preform to a temperature at which the glass viscosity is sufficiently low (e.g., less than 108 Poise) to draw fiber from the preform. Upon drawing, the preform necks down to a fiber that has the same cross-sectional composition and structure as the preform. The diameter of the fiber is determined by the specific Theological properties of the fiber and the rate at which it is drawn.
Preforms can be made using many techniques known to those skilled in the arts, including modified chemical vapor deposition (MCVD) and outside deposition (OVD). The MCVD process involves depositing layers of vaporized raw materials onto the inside walls of a pre-made tube in the form of soot. Each soot layer is fused shortly after depositing into a glass layer. This results in a preform tube that is subsequently collapsed into a solid rod, over jacketed, and then drawn into fiber.
The OVD process involves deposition of raw materials onto a rotating rod. This occurs in two steps: laydown and consolidation. During the laydown step, a soot preform is made from utlra-pure vapors of e.g., silicon tetrachloride (for silica fiber) and germanium tetrachloride. The vapors move through a traversing burner and react in the flame to form soot particles of silicon oxide and germanium oxide. These particles are deposited on the surface of the rotating target rod. When deposition is complete, the rod is removed, and the deposited material is placed in a consolidation furnace. Water vapor is removed, and the preform is collapsed to become a dense, transparent glass.
Another method for making a fiber preform is to simply insert a rod of one material into the core of a hollow preform. Heating consolidates the preform into a single object.
Fiber waveguides form the basis of numerous optical devices in addition to simply providing a channel for the transmission of optical information. For example, fiber waveguides can be design to compensate for effects that may be deleterious to an optical signal, e.g., dispersion. Dispersion is the property of a waveguide that causes optical signals of different wavelengths to travel at different speeds, which results in broadening of optical pulses. Typically, a long haul silica optical fiber has a positive dispersion of 2-50 ps/nm-km for wavelengths in the range of 1.5 xcexcm. This positive dispersion can be compensated by directing the signal through a waveguide having negative dispersion equal in magnitude to the positive dispersion introduced by the silica optical fiber. Often, this is implemented by providing alternating sections of fiber having positive and negative dispersion in an optical telecommunications network.
Another example of an effect that may be deleterious to an optical signal is attenuation. Attenuation is simply the loss of intensity of an optical signal that occurs as a signal propagates through an optical fiber. When attenuation is sufficiently large, the optical signal becomes indistinguishable from the background noise. Accordingly, important components in communications networks are fiber amplifiers. As their name implies, fiber amplifiers are fiber waveguides that amplify the signal strength of an optical signal. The growth of dense wavelength-division multiplexing applications, for example, has made erbium-doped fiber amplifiers (EDFA""s) an essential building block in modern telecommunication systems. EDFA""s amplify an optical signal inside a fiber and therefore allow transmission of information over longer distances without the need for conventional repeaters. To form an EDFA, the fiber is doped with erbium, a rare earth element, that has appropriate energy levels in its atomic structure to amplify light at 1550 nm. A 980 nm pump laser is used to inject energy into the erbium-doped fiber. When a weak signal at 1550 nm enters the fiber, the light stimulates the erbium atoms to release their stored energy as additional 1550 nm light. This stimulated emission is coherent with the original signal, and hence the original signal grows stronger in intensity as it propagates down the fiber.
A fiber laser is another example of an optical component made using optical fibers. Typically, the cavity is defined in the radial direction by the index difference between a high index core and a lower index cladding which confines EM radiation through total internal reflection (TIR). The cavity may be defined in the axial direction by reflectors. The end reflectors in early fiber lasers were mirrors placed at, or evaporated onto, the ends of polished fibers. Refractive index modulations along the fiber axis can also be used to create a reflector and thus define a lasing cavity. For example, two Bragg gratings can surround a gain medium and define the end reflectors, thereby forming a distributed Bragg reflector (DBR) laser. Alternatively, the axial modulation can extend through out the length of the gain medium to form a xe2x80x9cdistributed feedbackxe2x80x9d (DFB) laser.
The composition of typical fiber waveguides often consists of a single material, having an appropriately doped cross-sectional profile to manipulate the fiber""s optical properties. However, compositions including different materials may also be used. Accordingly, compositions including dissimilar materials, fiber waveguides derived from the dissimilar material compositions, and exemplary devices are disclosed.
The invention features high index-contrast fiber waveguides that can be drawn from a preform. The invention also features materials for forming high index-contrast fiber waveguides, and guidelines for their selection. High index-contrast fiber waveguides, which may include optical fibers (i.e., fiber waveguides that utilize total internal reflection to confine light to a core) and photonic crystal fibers (e.g., Bragg fibers), can provide enhanced radial confinement of an optical signal in the fiber waveguide. The enhanced radial confinement can reduce radiative losses, thereby improving transmission efficiency. Moreover, large optical energy densities can be achieved inside the high index-contrast fiber waveguides, making them attractive candidates for a number of applications, e.g., nonlinear applications. Moreover, in addition to enhanced radial confinement, it is also possible to achieve enhanced axial confinement in the fiber waveguide. Using the enhanced axial confinement and enhanced radial confinement, one can form optical cavities having high Q values and/or small modal volumes in high index-contrast fiber waveguides. These cavities can form the basis of many optical devices, e.g., bi-stable devices.
We will now summarize different aspects, features, and advantages of the invention.
In general, in one aspect, the invention features a fiber waveguide having a waveguide axis. The fiber waveguide includes a first portion extending along the waveguide axis including a first material having an index of refraction, n1, a working temperature, Tw, and a softening temperature, Ts. The fiber waveguide also includes a second portion extending along the waveguide axis comprising a second material having an index of refraction, n2, and a viscosity, xcex72, that varies as a function of temperature, T, and the absolute difference between n1 and n2 is at least 0.35 (e.g., at least 0.5, at least 0.6, at least 0.7, at least 0.8, at least 0.9, at least 1.0, at least 1.1, at least 1.2, at least 1.3, at least 1.4, at least 1.5, at least 1.6, at least 1.7, at least 1.8) and xcex72 at Tw is at least 103 Poise (e.g., at least 104 Poise) and no more than 106 Poise (e.g., no more than 105 Poise), and xcex72 at Ts is at least 105 Poise (e.g., at least 106 Poise, at least 107 Poise, at least 108 Poise, at least 109 Poise, at least 1010 Poise, at least 1011 Poise) and no more than 1013 Poise (e.g., no more than 1012 Poise, no more than 1011 Poise, no more than 1010 Poise, no more than 109 Poise, no more than 108 Poise).
Embodiments of the fiber waveguides can include on or more of the following features, and/or any of the features mentioned with respect to any other aspect of the invention.
The first and/or second materials can be dielectric materials, such as glasses. The first material can include a chalcogenide glass, and the second material can include an oxide glass and/or a halide glass.
The first and second portions can be homogeneous portions or inhomogeneous portions. Inhomogeneous portions can include at least one hollow region extending along the waveguide axis.
The first and/or second materials can be inorganic materials, such as polymers.
The first portion can be a core and n1 greater than n2, and the second portion can include a cladding layer.
The fiber waveguide can be a photonic crystal fiber, such as a Bragg fiber.
In some embodiments, the first portion can have a glass transition temperature, Tg, and xcex72 at Tg is at least 108 Poise (e.g., at least 109 Poise, at least 1010 Poise, at least 1011 Poise, at least 1012 Poise, at least 1013 Poise).
The first material can have a first thermal expansion coefficient, TEC1, and the second material has a second thermal expansion coefficient, TEC2, and between 20xc2x0 C. and 380xc2x0 C. |TEC1xe2x88x92TEC2|xe2x89xa65xc3x9710xe2x88x926/xc2x0 (e.g., |TEC1xe2x88x92TEC2|xe2x89xa64xc3x9710xe2x88x926/xc2x0, |TEC1xe2x88x92TEC2|xe2x89xa63xc3x9710xe2x88x926/xc2x0, |TEC1xe2x88x92TEC2|xe2x89xa62xc3x9710xe2x88x926/xc2x0, |TEC1xe2x88x92TEC2|xe2x89xa61xc3x9710xe2x88x926/xc2x0).
The residual stress between the first portion and second portion at 20xc2x0 C. can be less than 100 MPa (e.g., less than 80 MPa, less than 50 MPa, less than 40 MPa, less than 30 MPa, less than 20 MPa).
The fiber waveguide can include a confinement region, and the confinement region can include the first and second portions. The first portion can include a first layer extending along the waveguide axis and the second portion can include a second layer extending along the waveguide axis and surrounding the first layer.
The fiber waveguide can include an optical modulation extending along the waveguide axis. The optical modulation can include a structural modulation and/or a refractive index modulation.
In a second aspect, the invention features a method for making a fiber waveguide having a waveguide axis. The method includes providing a fiber preform including a first portion and a second portion surrounding the first portion. The first portion includes a first material having a refractive index n1 and the second portion includes a second material having a refractive index n2, and |n1xe2x88x92n2xe2x89xa70.3 (e.g., |n1xe2x88x92n2|xe2x89xa70, |n1xe2x88x92n2| greater than 0.). The method further includes heating the fiber preform to a temperature where the first and second portions have a viscosity between 103 Poise and 106 Poise, and drawing the heated fiber preform into the fiber waveguide.
Embodiments of the method can include any of the features mentioned with respect to other aspects of the invention, and/or one or more of the following features.
The fiber perform can be heated so that the first and second portions have a viscosity between 103 Poise and 105 Poise, such as about 104 Poise.
The first portion can include a preform core. The second portion can include a preform cladding.
The fiber preform can include a preform confinement region, and the first and second portions can be included in the fiber preform.
The first material can include a first glass (e.g., a chalcogenide glass) and the second material can include a second glass different from the first glass (e.g., an oxide glass or a halide glass).
The method can further include perturbing the fiber waveguide while drawing to form an optical modulation extending along the waveguide axis of the fiber waveguide.
The relative cross sectional structure of the fiber preform can be preserved during the drawing.
In a further aspect, the invention features a fiber waveguide having a waveguide axis including a first portion extending along the waveguide axis. The fiber waveguide also includes a second portion different from the first portion extending along the waveguide axis surrounding the first portion, and at least one of the first and second portions includes a chalcogenide glass selected from the group consisting of Selenium chalcogenide glasses and Tellurium chalcogenide glasses.
Embodiments of the fiber waveguide can include any of the features mentioned with respect to other aspects of the invention and/or one or more of the following features.
The chalcogenide glass can be any of the following glasses: Asxe2x80x94Se, Gexe2x80x94Se, Asxe2x80x94Te, Sbxe2x80x94Se, Asxe2x80x94Sxe2x80x94Se, Sxe2x80x94Sexe2x80x94Te, Asxe2x80x94Sexe2x80x94Te, Asxe2x80x94Sxe2x80x94Te, Gexe2x80x94Sxe2x80x94Te, Gexe2x80x94Sexe2x80x94Te, Gexe2x80x94Sxe2x80x94Se, Asxe2x80x94Gexe2x80x94Se, Asxe2x80x94Gexe2x80x94Te, Asxe2x80x94Sexe2x80x94Pb, Asxe2x80x94Sexe2x80x94Tl, Asxe2x80x94Texe2x80x94Tl, Asxe2x80x94Sexe2x80x94Ga, and Gexe2x80x94Sbxe2x80x94Se. The chalcogenide glass can be As12Ge33Se55.
The chalcogenide glass can include any of the following elements: boron, aluminum, silicon, phosphorus, sulfur, gallium, arsenic, indium, tin, antimony, thallium, lead, bismuth, cadmium, lanthanum, fluorine, chlorine, bromine, and iodine.
Either or both of the first and second portions can include a nonlinear material (e.g., an electrooptic material and/or a photorefractive material). Either or both portions can be doped with one or more rare earth ions (e.g. erbium ions).
The second portion can include a dielectric material, such as an organic or inorganic dielectric material. The inorganic material can be an inorganic glass (e.g., an oxide, halide glass or mixed oxide-fluoride glass). In cases where the inorganic material is an oxide glass, the oxide glass can include up to 40 mole % (e.g., up to 30%, up to 20%, up to 10%, up to 5%) of a compound of the form MO, where M can be Pb, Ca, Mg, Sr, and Ba. The oxide glass can include up to 40 mole % (e.g., up to 30%, up to 20%, up to 10%, up to 5%) of a compound of the form M2O, where M can be Li, Na, K, Rb, and Cs. The oxide glass can include up to 40 mole % (e.g., up to 30%, up to 20%, up to 10%, up to 5%) of a compound of the form M2O3, where M can be Al, B, and Bi. The oxide glass can also include up to 60 mole % (e.g., up to 50%, up to 40%, up to 30%, up to 20%, up to 10%, up to 5%) of P2O5. The oxide glass can further include up to 40 mole % (e.g., up to 30%, up to 20%, up to 10%, up to 5%) of SiO2.
In embodiments where the dielectric material is an organic material, the organic material can be a polymer (e.g., carbonate-, sulfone-, etherimid-, and/or acrylate- family polymer, and/or fluoropolymers).
The first portion can be a core having a refractive index n1 and the second portion has a refractive index n2 less than n1.
The fiber waveguide can be a photonic crystal fiber, such as a Bragg fiber or holey photonic crystal fiber.
In another aspect, the invention features a fiber waveguide having a waveguide axis, including a core extending along the waveguide axis, and a confinement region extending along the waveguide axis surrounding the core, the confinement region including a chalcogenide glass. The confinement region further a photonic crystal structure having a photonic band gap, wherein during operation the confinement region guides EM radiation in at least a first range of frequencies to propagate along the waveguide axis.
Embodiments of the fiber waveguide can include any of the features mentioned with respect to other aspects of the invention, and/or one or more of the following features.
The confinement region can include a first portion having a refractive index n1 and a second portion having a refractive index n2, and |n1xe2x88x92n2|xe2x89xa70. (e.g., |n1xe2x88x92n2|xe2x89xa70. , |n1xe2x88x92n2|xe2x89xa70. , |n1xe2x88x92n2|xe2x89xa70., |n1xe2x88x92n2|xe2x89xa70., |n1xe2x88x92n2|xe2x89xa70., |n1xe2x88x92n2|xe2x89xa70.).
The core can be a hollow core. The core can include a dielectric material, such as the dielectric materials listed above.
The confinement region can include a plurality of layers. These layers can include alternating layers including the chalcogenide glass, such as a chalcogenide glass listed above. A subset of the plurality of layers can be devoid of the chalcogenide glass. The subset of layers can be alternating layers.
In a further aspect, the invention features a method for making an fiber waveguide, including providing a fiber preform including a first portion and a second portion surrounding the first portion, wherein the first portion includes a chalcogenide glass. The method also includes heating the fiber preform so that the first and second portions have a viscosity between 103 Poise and 106 Poise, and drawing the heated fiber preform to make the fiber waveguide.
Embodiments of the method can include any of the features mentioned with respect to other aspects of the invention.
In general, in another aspect, the invention features a fiber waveguide having a waveguide axis, including a core extending along the waveguide axis including a first dielectric material having a refractive index n1, and a cladding extending along the waveguide axis and surrounding the core, the cladding including a second dielectric material having a refractive index n2 less than n1. Also, the fiber waveguide has a numerical aperture greater than 0.7 (e.g., greater than 0.8, greater than 0.9, greater than 1.0, greater than 1.1, greater than 1.2, greater than 1.3, greater than 1.4, greater than 1.5).
Embodiments of the fiber waveguide can include any of the features mentioned with respect to other aspects of the invention, and/or any of the features listed below.
The refractive index of the first dielectric material can be more than 1.8, (e.g., more than 1.9, more than 2.0, more than 2.1, more than 2.2, more than 2.3, more than 2.4, such as about 2.5).
The core can include an optical modulation extending along the waveguide axis (e.g., a refractive index modulation and/or a structural modulation). The optical modulation can cause the optical fiber to have a transmission bandgap of at least 0.1% (e.g., at least 1%, at least 2%, at least 3%, at least 4%, at least 5%, such as 6% or more).
For at least one wavelength the fiber can have a mode field diameter less than 3 microns (e.g., less than 2 microns, less than 1 micron, less than 0.5 microns, less than 0.25 microns).
The refractive index of the second dielectric material can be less than 1.9 (e.g., less than 1.8, less than 1.7, less than 1.6, less than 1.5, such as about 1.4).
The fiber waveguide can further include a dispersion tailoring region extending along the waveguide axis, can during operation the core can support at least one mode in a range of frequencies and the dispersion tailoring region introduces one or more additional modes in the first range of frequencies that interact with the guided mode to produce a working mode. The cladding can surround the dispersion tailoring region.
The core can have a diameter less than 3 microns (e.g., less than 2 microns, less than 1 micron, less than 0.5 microns, less than 0.25 microns).
In a further aspect, the invention features a fiber waveguide having a waveguide axis, including a first portion extending along the waveguide axis including a first material having a refractive index n1 and a melting temperature, Tm. The fiber waveguide also includes a second portion extending along the waveguide axis that surrounds the first portion and includes a second material that has a refractive index n2 and a working temperature, Tw, and |n1xe2x88x92n2|xe2x89xa70.3 and Tm greater than Tw.
Embodiments of the fiber waveguide can include any of the features mentioned with respect to other aspects of the invention.
In another aspect, the invention features an optical fiber having a waveguide axis, including a core extending along the waveguide axis comprising a first dielectric material having a refractive index n1, and a cladding extending along the waveguide axis and surrounding the core. The cladding can include a second dielectric material having a refractive index n2, and n1xe2x88x92n2xe2x89xa70. (e.g., n1xe2x88x92n2xe2x89xa70., n1xe2x88x92n2xe2x89xa70., n1xe2x88x92n2xe2x89xa70., n1xe2x88x92n2xe2x89xa71., n1xe2x88x92n2xe2x89xa71., n1xe2x88x92n2xe2x89xa71.).
Embodiments of the optical fiber can include any of the features mentioned with respect to other aspects of the invention.
In a further aspect, the invention features a method, including providing a fiber waveguide having a waveguide axis that includes a first portion extending along the waveguide axis having a refractive index n1, and a second portion extending along the waveguide axis having a refractive index n2, in which |n1xe2x88x92n2xe2x89xa70.3. The method also includes directing an input signal into the fiber waveguide with an input signal power sufficient to cause the fiber waveguide to produce an output signal whose output signal power varies nonlinearly with respect to the input signal power.
Embodiments of the method can include any of the features mentioned with respect to other aspects of the invention.
In general, in another aspect, the invention features a method for making a photonic crystal fiber having an axial optical modulation along a waveguide axis. The method includes heating a photonic crystal fiber preform to a draw temperature, drawing the photonic crystal fiber from the preform, and perturbing the photonic crystal fiber preform during the drawing to produce an axial optical modulation in the photonic crystal fiber along the waveguide axis.
Embodiments of the method can include one or more of the features mentioned with respect to other aspects of the invention, and/or any of the following features.
The photonic crystal fiber can include a first layer extending along the waveguide axis having a first refractive index, n1 and a second layer extending along the waveguide axis adjacent the first layer having a second refractive index, n2, and |n1xe2x88x92n2xe2x89xa70. (e.g., |n1xe2x88x92n2|xe2x89xa70., |n1xe2x88x92n2|xe2x89xa70., |n1xe2x88x92n2|xe2x89xa70., |n1xe2x88x92n2|xe2x89xa70.).
The photonic crystal fiber can have a hollow core.
The diameter of the photonic crystal fiber can be related to a drawing velocity and perturbing the fiber can include varying the fiber diameter by varying the drawing velocity.
Perturbing the photonic crystal fiber can include varying the drawing temperature along the waveguide axis to vary the photonic crystal fiber diameter. The photonic crystal fiber can be illuminated with radiation (e.g., laser radiation) during drawing to vary the drawing temperature along the waveguide axis.
The photonic crystal fiber can be a hollow fiber, and perturbing the fiber can include varying the pressure inside the hollow fiber. Alternatively, or additionally, perturbing the fiber can include varying the pressure outside the photonic crystal fiber.
The axial optical modulation can be a periodic or aperiodic modulation. The axial optical modulation can form a fiber Bragg grating in the photonic crystal fiber.
The axial optical modulation can form an optical cavity in the photonic crystal fiber.
In a further aspect, the invention features a method for forming an axial optical modulation along a waveguide axis of a fiber waveguide. The method includes providing a fiber waveguide having a hollow core, introducing a core medium into the hollow core; and exposing the fiber waveguide to an agent that causes the core medium to form an axial optical modulation along the waveguide axis of the fiber waveguide.
Embodiments of the method can include one or more of the features mentioned with respect to other aspects of the invention, and/or any of the following features.
The core medium can include a plurality of similarly-shaped objects (e.g., spherical objects). The similarly-shaped objects can be polymeric objects. At least a portion of the similarly-shaped objects can be positioned adjacent one another in the hollow core. Exposing the fiber waveguide to an agent can include heating the fiber to cause the fiber waveguide to conform to the plurality of similarly-shaped objects in the hollow core.
The method can include removing at least a portion of the core medium after exposing the waveguide fiber to the agent. Removing the core medium can include providing a removal agent (e.g., an etchant or solvent) in the core that removes the portion of the core medium.
The core medium can be a photosensitive medium (e.g., a photoresist, or material whose refractive index changes on exposure to radiation).
Exposing the core medium to an agent can include illuminating portions of the core medium to radiation (e.g., electromagnetic radiation or electron beam radiation). The radiation can include an interference pattern. The radiation can cause an optical property (e.g., the refractive index of the core medium, or the structure of the core medium) of the exposed portions of the core medium to be different from the optical properties of portions not exposed to radiation.
The core medium can be a block co-polymer.
In another aspect, the invention features a fiber waveguide having a waveguide axis, including a first portion extending along the waveguide axis having a refractive index n1, and a second portion extending along the waveguide axis having a refractive index n2, and |n1xe2x88x92n2|xe2x89xa70.3. Also, the fiber waveguide has an axial optical modulation extending along the waveguide axis.
Embodiments of the fiber waveguide can include one or more of the features mentioned with respect to other aspects of the invention, and/or any of the following features.
The axial optical modulation can have an amplitude of at least 0.1% (e.g., at least 0.5%, at least 1%, at least 2%, at least 3%, at least 4%, at least 5%, at least 6%, at least 7%, such as 8% or more).
The axial optical modulation can include a structural modulation, such as a modulation in the fiber waveguide diameter. The axial optical modulation can be a modulation in the fiber waveguide refractive index.
The axial optical modulation can form a Bragg reflector in the fiber waveguide. The axial optical modulation forms an optical cavity in the fiber waveguide. The optical cavity has a resonant wavelength, xcex, and a modal volume less than or equal to 500 xcex3 (e.g., less than or equal to 200 xcex3, less than or equal to 100 xcex3, less than or equal to 50 xcex3, less than or equal to 20 xcex3, less than or equal to 10 xcex3, less than or equal to 5 xcex3, less than or equal to 2 xcex3, less than or equal to 1 xcex3).
The second portion can surround the first portion and the first portion can include a nonlinear material.
In another aspect, the invention features an optical fiber having a waveguide axis, including a core extending along the waveguide axis having a refractive index, n1, and a cladding extending along the waveguide axis and surrounding the core, the cladding having a refractive index n2 less than n1; and an axial optical modulation extending along the waveguide axis forming an optical cavity having a resonant wavelength xcex, and a modal volume of less than or equal to 100 xcex3 (e.g., less than 50 xcex3, less than 20 xcex3, less than 10 xcex3, less than 5 xcex3, less than 2 xcex3, less than 1 xcex3).
Embodiments of the optical fiber can include one or more of the features mentioned with respect to other aspects of the invention, and/or any of the following features.
The axial optical modulation can have an amplitude of at least 1% (e.g., at least 2%, at least 3%, at least 4%, at least 5%).
In another aspect, the invention features a fiber waveguide device, including a fiber waveguide having a waveguide axis, and the fiber waveguide includes a first portion extending along the waveguide axis having a refractive index n1, and a second portion extending along the waveguide axis having a refractive index n2, and |n1xe2x88x92n2|xe2x89xa70.3. The fiber waveguide device also includes an axial optical modulation forming an optical cavity in the fiber waveguide and during operation an input signal propagating in the fiber waveguide having a power between a first power value, P1, and a second power value, P2, causes the fiber waveguide to produce an output signal whose output signal power varies nonlinearly with respect to the input signal power.
Embodiments of the fiber waveguide device can include one or more of the features mentioned with respect to other aspects of the invention, and/or any of the following features.
An input signal power between P1 and P2 can cause the fiber waveguide to produce an output signal whose output signal power varies discontinuously with respect to the input signal power.
An input signal power below P1 can cause the fiber waveguide to produce an output signal whose output signal power is below an output power value Pout,1, and an input signal power above P2 can cause the fiber waveguide to produce an output signal whose output signal power is above an output power value Pout,2, where Pout,2/Pout,1 is at least 2 (e.g., at least 5, at least 10, at least 100). The ratio P1/P2 can be greater than 0.5 (e.g., greater than 0.75, greater than 0.9, greater than 0.95, greater than 0.99).
The optical cavity has a quality factor Q and P1 can be less than or equal to 108 W/Q2 (e.g., less than or equal to 107 W/Q2.106 W/Q2 105 W/Q2 104 W/Q2 103 W/Q2).
The axial optical modulation can form more than one optical cavity (e.g., two optical cavities, three optical cavities, four optical cavities, or five or more optical cavities).
In a further aspect, the invention features a photonic crystal fiber having a waveguide axis, including a core region extending along the waveguide axis, a confinement region extending along the waveguide axis and surrounding the core and including a chalcogenide glass, and an axial optical modulation extending along waveguide axis forming an optical cavity in the photonic crystal fiber.
Embodiments of the photonic crystal fiber can include one or more of the features mentioned with respect to other aspects of the invention, and/or any of the following features.
The photonic crystal fiber can be a one-dimensionally periodic photonic crystal fiber (e.g., a Bragg fiber). The photonic crystal fiber can be a two-dimensionally periodic photonic crystal fiber, e.g., having an inhomogeneous confinement region, such as a holey region.
The axial optical modulation can have an amplitude of at least 0.01%.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the apparatus, methods, and examples are illustrative only and not intended to be limiting.
Additional features, objects, and advantages of the invention will be apparent from the following detailed description and drawings, and from the claims.